[R] set.seed

[Jim_Garrett@bd.com]

I'm running into problems with set.seed--maybe I'm misunderstanding
something.

I'm running R 1.5.1 on Windows 2000.

I'm basically trying to capture the random seed so that I can reproduce a
simulation if it's necessary later.  Using set.seed, I can certainly get
reproducible results, but not the results I get on the first pass.  Here's
an example:

# Generate a random number to initialize
> runif(1)
[1] 0.965875
> RNGkind()
[1] "Marsaglia-Multicarry" "Kinderman-Ramage"
>
> # Save random seed
> temp.seed <- .Random.seed
>
> # Proceed to generate random uniforms
> runif(5)
[1] 0.18734034 0.02723140 0.46396251 0.10602243 0.64362777
>
> # try to reproduce this sequence
> set.seed(temp.seed, "default")
> runif(5)
[1] 0.006153224 0.553233950 0.091852441 0.643058504 0.009685173
>
> # just to see, try again
> set.seed(temp.seed, "default")
> runif(5)
[1] 0.006153224 0.553233950 0.091852441 0.643058504 0.009685173

So you can see that I can reproduce the latter sequence, but not the first
sequence.  As a workaround, I guess I can call set.seed prior to generating
the first sequence.  But it puzzles me why capturing the random seed
appears not to be sufficient.  Am I overlooking something?

Thanks for any guidance.

Jim Garrett
Becton Dickinson Diagnostic Systems
Baltimore, Maryland, USA


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